Condensates of ethane-1-hydroxyl-1,1-diphosphonic acid are known such as those described in U.S. Pat. Nos. 3,387,024; 3,400,151 and 3,621,081. In the first two noted patents, the condensates are limited to dimers of ethane-1-hydroxy-1,1-diphosphonates joined by C-O-C bonds or P-O-P bonds, as opposed to the oligomeric ester compounds of the present invention which contain C-O-P bonds. While the latter mentioned patent U.S. Pat. No. 3,621,081 to Prentice does disclose oligomeric ester compounds of phosphorus acid which contain C-O-P bonds, the patent specifically limits the compounds to those containing a methyl end group. Not only were the preparatory methods of Prentice found to be unsuitable for preparation of the C.sub.6 -C.sub.13 compounds of the present invention, but the higher homologs were unexpectedly found to possess "reverse" emulsion breaking properties not found in the Prentice oligomer.